Variable speed pipeline pig with internal flow cavity

ABSTRACT

A pipeline pig includes a plurality of relief channels and a bypass channel extending therethrough. To regulate a speed of the pipeline pig, relief valves within the relief channels open when a differential pressure between upstream and downstream ends of the pipeline pig reaches a pre-selected minimum relief pressure. If the differential pressure reaches a pre-selected maximum relief pressure, such as when the pipeline pig encounters an obstruction, the relief valves close to allow the differential pressure to further increase to clear the obstruction. If the further increase in differential pressure is insufficient to clear the obstruction and the differential pressure reaches a pre-selected minimum bypass pressure, a bypass valve opens to permit fluid flow through the bypass channel while the relief valves are closed. Flow through the bypass channel operates to reduce turbulence and permit production through the pipeline if the pipeline pig becomes stuck and obstructs the pipeline.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate generally to a pipeline pigthat is propelled by the pressure of a pipeline fluid flowing through apipeline. In particular, embodiments of the invention relate to apipeline pig with a plurality of distinct flow channels extendingtherethrough that selectively permit and prohibit flow of the pipelinefluid through the pipeline pig.

2. Description of the Related Art

An instrument for inspecting, cleaning, and maintaining a pipeline isoften referred to as a pipeline pig. In some applications, the pipelinepig is propelled along an interior of the pipeline under the pressure ofa pipeline fluid flowing through the pipeline. To facilitate advancementof the pipeline pig, one or more flexible guide disks or cups are oftenprovided that extend outwardly from a longitudinal body of the pipelinepig. The flexible guide disks extend to an interior wall of the pipelineso as to form a seal between the pipeline and the pipeline pig. If theseal is substantially complete, the pipeline pig is induced to travel atthe speed of the pipeline fluid. In some applications, flow channels areprovided through the pipeline pig to permit a portion of the pipelinefluid to flow through the pipeline pig, thereby regulating the speed ofthe pipeline pig.

Buildup of debris within the pipeline can be problematic for theoperation of the pipeline pig. Debris ahead of the pig may slow thepipeline pig below a minimum speed required for carrying out the desiredapplication, or in some instances, can completely prevent the pipelinepig from moving forward through the pipeline. Also, flow channels forregulating a speed of the pipeline pig reduce the maximum fluid forcethat can be applied to the pipeline pig to drive it through thepipeline, and thus can increase the likelihood that the pipeline pigwill become stuck in the pipeline when debris or other obstructions areencountered. If the pipeline pig becomes stuck in the pipeline, flow ofthe pipeline fluid can be restricted or impeded. Often, contingencyplans to recover the pipeline pig include cutting the pipeline at thepoint where the pig is stuck in order to remove it. Once the pig isremoved, the pipeline is then reconnected and put back in service. Thiscontingency plan is costly due to inhibited pipeline flow and downtimewhile the pipeline is cleared.

SUMMARY OF THE INVENTION

Described herein are systems and methods for controlling a flow ofpipeline fluid through a pipeline pig. Embodiments of the systems andmethods include relief channels that can be selectively opened andclosed to regulate both the speed of the pipeline pig and the fluidforce available behind the pipeline pig for clearing obstructions aheadof the pipeline pig. Flow of the pipeline fluid can be diverted from therelief channels to a central bypass channel to permit continuedproduction through the pipeline in the event the force required to clearan obstruction is unsafe for the pipeline pig or the pipeline.

According to one aspect of the invention, a pipeline pig includes ahousing defining a trailing end, a leading end and longitudinal axisextending therebetween. A bypass channel extends longitudinally throughthe housing between the trailing end and the leading end. A bypass valveis disposed within the bypass channel. The bypass valve is operable tomaintain a restrictive configuration in which a pipeline fluid isprohibited from flowing through the bypass channel when a differentialpressure established in the pipeline fluid between the trailing end andthe leading end of the housing is below a pre-selected minimum bypasspressure. The bypass valve is also operable to move to a bypassconfiguration in which the pipeline fluid is permitted to flow throughthe bypass channel in response to the differential pressure reaching thepre-selected minimum bypass pressure. At least one relief channelextends longitudinally through the housing between the trailing end andthe leading end. At least one relief valve is disposed within the atleast one relief channel, and is operable to move from a first closedconfiguration to an open configuration in response to the differentialpressure reaching a pre-selected minimum relief pressure. The at leastone relief valve is also operable to move from the open configuration toa second closed configuration in response to the differential pressurereaching a pre-selected maximum relief pressure. The at least one reliefvalve prohibits flow of the pipeline fluid through the at least onerelief channel when in the first and second closed configurations andpermits flow of the pipeline fluid through the at least one reliefchannel when in the open configuration. The pre-selected minimum bypasspressure is greater than the pre-selected maximum relief pressure, andthe pre-selected maximum relief pressure is greater than thepre-selected minimum relief pressure.

In some embodiments, the at least one relief valve includes a closuremember that is respectively movable between first and second seats tomove the at least one relief valve between the first and second closedconfigurations. The closure member is biased toward the first seat andaway from the second seat by a biasing member such that the biasingmember defines the pre-selected minimum relief pressure and thepre-selected maximum relief pressure. In some embodiments, thepre-selected minimum relief pressure is in the range of 1 psi to 3 psiand the pre-selected maximum relief pressure is in the range of 4 psi to6 psi. In some embodiments the pre-selected minimum bypass pressure isgreater than 90 psi.

In some embodiments, the bypass channel is centrally disposed within thehousing, and the at least one relief channel includes a plurality ofrelief channels radially disposed about the bypass channel.

In some embodiments, the bypass channel includes a tapering constrictiontherein such that the bypass channel defines a venturi. The taperingconstriction is defined between an outer wall of the bypass channel anda closure member of the bypass valve disposed within the bypass channel.The closure member is operable to move the bypass valve between therestrictive configuration and the bypass configuration. The bypass valvefurther includes a biasing member operable to maintain the closuremember in contact with a bypass seat to maintain the bypass valve in therestrictive configuration. The biasing member is responsive to thedifferential pressure to adjust the size of the tapering constriction.

In some embodiments, the bypass valve includes an inner wall extendingthrough at least a portion of the bypass channel, and the closure memberis arranged to form a tapered profile with the inner wall when thebypass valve is in the bypass configuration.

According to another aspect of the invention, a pipeline pig includes ahousing defining a trailing end, a leading end and longitudinal axisextending therebetween. At least one relief channel extendslongitudinally through the housing between the trailing end and theleading end, and the at least one relief channel defines an annularwall. A closure member is disposed within the annular wall, and theclosure member is operable to engage a first seat to restrict fluid flowthrough the relief channel and operable to disengage the first seat topermit fluid flow through the relief channel. An annular space isdefined between the closure member and the annular wall. The annularspace exhibits a smaller cross-section than regions of relief channelupstream and downstream of the closure member such that the annularspace represents a constriction for fluid flow, and the relief channeldefines a venturi.

In some embodiments, the closure member is further operable to engage asecond seat to restrict fluid flow through the relief channel while theclosure member is disengaged from the first seat. The closure member isbiased toward the first seat and away from the second seat by a biasingmember such that the biasing member is operable to passively maintainthe closure member in engagement with the first seat if a differentialpressure established between a trailing end and a leading end of thehousing is less than a pre-selected minimum relief pressure. The biasingmember is also operable to permit the closure member to engage thesecond seat if the differential pressure is greater than a pre-selectedmaximum relief pressure.

In some embodiments, the pipeline pig further includes a bypass channeland a bypass valve. The bypass channel extends longitudinally throughthe housing between the trailing end and the leading end thereof, andthe bypass valve is operable to selectively move between restrictive andbypass configurations to respectively restrict and permit fluid flowthrough the bypass channel. The bypass valve is operable move from therestrictive configuration to the bypass configuration in response to thedifferential pressure reaching a pre-selected minimum bypass pressure,and the pre-selected minimum bypass pressure is greater than thepre-selected maximum relief pressure such that the bypass valve moves tothe bypass configuration while the closure member is engaged with thesecond seat and fluid flow through the at least one relief channel isrestricted.

In some embodiments, the closure member is operably coupled to anactuator, and the actuator is operable to move the closure member intoengagement with the first seat if a differential pressure establishedbetween a trailing end and a leading end of the housing is less than apre-selected minimum relief pressure, and operable to move the closuremember into engagement with the second seat if the differential pressureis greater than a pre-selected maximum relief pressure.

According to another aspect of the invention, a method of controlling aflow of pipeline fluid through a pipeline pig that includes a bypasschannel and at least one relief channel extending therethrough includesthe steps of (a) inserting the pipeline pig into a pipeline throughwhich the pipeline fluid is flowing, (b) increasing a differentialpressure established in the pipeline fluid between a trailing end and aleading end of the pipeline pig such that the differential pressuresequentially reaches a pre-selected minimum relief pressure, apre-selected maximum relief pressure and a pre-selected minimum bypasspressure, (c) opening the at least one relief valve to permit thepipeline fluid to flow through the relief channel when the differentialpressure reaches the pre-selected minimum relief pressure (d) closingthe at least one relief valve to restrict the flow of pipeline fluidthrough the relief channel when the differential pressure reaches apre-selected maximum relief pressure, and (e) opening a bypass valve topermit the pipeline fluid to flow through the bypass channel when thedifferential pressure reaches the pre-selected minimum bypass pressure.

In some embodiments, the step of opening the at least one relief valveincludes compressing a compression spring to move a closure member outof contact with a first seat. The step of closing the at least onerelief valve includes further compressing the compression spring to movethe closure member into contact with a second seat.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features, aspects andadvantages of the invention, as well as others that will becomeapparent, are attained and can be understood in detail, a moreparticular description of the invention briefly summarized above may behad by reference to the embodiments thereof that are illustrated in thedrawings that form a part of this specification. It is to be noted,however, that the appended drawings illustrate only preferredembodiments of the invention and are, therefore, not to be consideredlimiting of the invention's scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a schematic cross-sectional side view of a pipeline pigincluding a passive bypass valve and a plurality of passive reliefvalves in accordance with an example embodiment of the presentinvention.

FIG. 1B is an end view of the pipeline pig of FIG. 1A.

FIGS. 2A through 2C are schematic side views of one of the relief valvesof FIG. 1A arranged respectively in a first closed configuration, anopen configuration and a second closed configuration, illustrating anexample sequence of operation in accordance with an example embodimentof the present invention.

FIGS. 3A and 3B are schematic side views of the bypass valve of FIG. 1Aarranged respectively in a restrictive configuration and bypassconfiguration.

FIG. 4 is a flow diagram illustrating a method of controlling a flow ofpipeline fluid through a pipeline pig in accordance with an exampleembodiment of the present invention.

FIG. 5 is a schematic cross-sectional side view of an a pipeline pigincluding active relief and bypass valves accordance with an alternateexample embodiment of the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings which illustrate embodiments ofthe invention. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

Referring to FIGS. 1A and 1B, pipeline pig 10 is constructed inaccordance with an example embodiment of the present invention, and isdisposed within an interior of pipeline “P.” Pipeline pig 10 includeshousing 12, which defines a downstream or leading end 14, an upstream ortrailing end 16 and longitudinal axis “A” extending therebetween. Apressure differential established in pipeline fluid “F” between leadingend 14 and trailing end 16 propels pipeline pig 10 through the interiorof pipeline “P.” As used herein, unless otherwise specified, the phrase“differential pressure” designates a relatively high pressure on anupstream side (generally designated in the figures by “U” (towardtrailing end 16)) of pipeline pig 10 with respect to a relatively lowpressure on a downstream side (generally designated in the figures by“D” (toward leading end 14)). A plurality of bracketed front guide discs18, and bracketed rear guide discs 20 are disposed about housing 12 atleading end 14 and trailing end 16 respectively. Bracketed front guidediscs 18 and bracketed rear guide disks 20 sealingly contact a wall ofpipeline “P” to scrape deposits therefrom and to guide pipeline pig 10through pipeline “P.” Pipeline pig 10 is propelled as pipeline fluid“F,” as indicated by arrows 22, push pipeline pig 10. In someembodiments, pinger 24 is included within or mounted to housing 12 ofpipeline pig 10. Pinger 24 is operable to provide a signal to facilitatedetermination of a location of pipeline pig 10 throughout deployment ofpipeline pig 10 in pipeline “P.”

Internal flow cavity 30 extends longitudinally through pipeline pig 10between trailing end 16 and leading end 14 of housing 12. Internal flowcavity 30 includes bypass channel 32 extending centrally therethroughand a plurality of distinct relief channels 34 radially disposed aboutbypass channel 32. In the embodiment illustrated, eight (8) reliefchannels 34 are provided although more or fewer are provided in otherembodiments. Bypass valve 42 is provided within bypass channel 32. Asdescribed in greater detail below, bypass valve 42 is operable toselectively restrict and permit flow of pipeline fluid “F” throughbypass channel 32. Relief valves 44 are provided within each reliefchannel 34. Relief valves 44 are operable to selectively restrict andpermit flow of pipeline fluid “F through respective relief channels 34.In the embodiment illustrated, bypass valve 42 and relief valves 44 arelongitudinally adjacent although, in other embodiments, bypass valve 42is disposed in an upstream position or in a downstream position withrespect to relief valves 44.

Referring now to FIGS. 2A through 2C relief valve 44 is selectivelymovable between at least three distinct configurations including a firstclosed configuration (FIG. 2A), an open configuration (FIG. 2B) and asecond closed configuration (FIG. 2C). Relief valve 44 includes closuremember 50 that is respectively movable between first seat 52 and secondseat 54 to move relief valve 44 between the first and second closedconfigurations. Closure member 50 is biased toward first seat 52 andaway from second seat 54 by biasing member 56. In the illustratedembodiment, biasing member 56 is a compression spring coupled betweenclosure member 50 and support plate 58, and is disposed in a downstreamposition with respect to closure member 50. Thus, biasing member 56provides a force to the closure member 50 in a direction opposite adirection of a flow of pipeline fluid “F” as indicated by arrow 22.

As illustrated in FIG. 2A, when a differential pressure between upstreamand downstream sides of closure member 50 is maintained below apre-selected minimum relief pressure, the force of biasing member 56 issufficient to maintain closure member 50 in sealing contact with firstseat 52. Upstream end 60 engages first seat 52 in the first closedconfiguration to form a metal-to-metal seal therewith. In someembodiments, upstream end 60 is constructed of a relatively softmaterial such as a brass or tin alloy to establish a fluid-tight sealwith relatively hard first seat 52, which is constructed of steel. Inother embodiments, other materials including elastomers or othernon-metallic materials such as polyetheretherketone (PEEK) polymers areprovided in at least one of upstream end 60 or first seat 52 tofacilitate formation of a fluid-tight seal.

When the differential pressure between upstream and downstream sides ofclosure member 50 reaches the pre-selected minimum relief pressure,relief valve 44 moves from the first closed configuration of FIG. 2A tothe open configuration of FIG. 2B. The pre-selected minimum reliefpressure is the pressure necessary for the pipeline fluid “F” pressingupon an upstream end 60 of closure member 50 to overcome the biasingforce of biasing member 50 that maintains upstream end 60 in sealingcontact with first seat 52. In some embodiments, the pre-selectedminimum relief pressure associated with each of relief valve 44 isequivalent, and is in the range of 1 psi to 3 psi. In other embodiments,each relief valve 44 is associated with an incremental pre-selectedminimum relief pressure such that relief valves 44 moves to the openconfiguration sequentially as the differential pressure increases. Insome embodiments, each pair of radially opposite relief valves 44 isassociated with the same pre-selected minimum relief pressure such thatopposing relief valves 44 move to the open configuration simultaneouslyto balance the flow of production fluid “F” through internal flow cavity30 (FIG. 1A).

As illustrated in FIG. 2B, upstream end 60 and downstream end 62 ofclosure member 50 each exhibit a hemispherical or bulbous profile, whichguides pipeline fluid “F” into and out of an annular space 64surrounding closure member 50. Annular space 64 is defined by annularwall 66 of bypass channel 34 with an increasing inner diameter fromfirst seat 52 and second seat 54 toward a longitudinally central regionof annular space 64. Annular space 64 exhibits smaller cross-sectionalarea than regions of relief channel 34 upstream and downstream ofclosure member 50, and thus, annular space 64 represents a constrictionfor fluid flow. A venturi is defined by this constriction in the flow ofpipeline fluid “F,” as will be appreciated by those skilled in the art.The shape of annular space 64 compliments the shape of upstream end 60and downstream end 62 to discourage turbulence in the flow of pipelinefluid “F” through relief channel 34 and thereby manage erosion ofannular wall 66, closure member 50 and other surfaces as appreciated bythose skilled in the art. Flow of pipeline fluid “F” through reliefchannel 34 serves to limit the speed of pipeline pig 10 (FIG. 1A)through pipeline “P.”

When the differential pressure in pipeline fluid “F” between upstreamand downstream sides of closure member 50 reaches a pre-selected maximumrelief pressure, relief valve 44 moves from the open configuration ofFIG. 2B to the second closed configuration of FIG. 2C. In someembodiments, the pre-selected maximum relief pressure associated withrelief valve 44 is in the range of 4 psi to 6 psi, as is often realizedwhen pipeline pig 10 encounters an obstruction or debris in pipeline “P”(FIG. 1A). Downstream end 62 engages second seat 54 in the second closedconfiguration to form a seal therewith. As one skilled in the art willappreciate, in some embodiments, downstream end 62 and second seat 52are constructed of any of the materials described above for theconstruction of upstream end 60 or first seat 52 to facilitate formationof a fluid-tight seal.

In the event that the differential pressure is reduced to below thepre-selected maximum relief pressure, as is often realized when anobstruction is cleared from pipeline “P” (FIG. 1A) downstream ofpipeline pig 10, biasing member 56 urges closure member 50 away fromsecond seat 54. For example, if the differential pressure is reduced toa level between the pre-selected minimum relief pressure and thepre-selected maximum relief pressure, biasing member 56 returns reliefvalve 44 to the open configuration of FIG. 2B, and if the differentialpressure is reduced to a level below the pre-selected minimum reliefpressure, biasing member 56 returns relief valve 44 to the first closedconfiguration of FIG. 2A. As one skilled in the art will appreciate,attributes of biasing member 56 such as a spring constant, length andpre-load, which are incorporated into the design of relief valve 44,define the pre-selected minimum relief pressure and the pre-selectedmaximum relief pressure. In this manner, relief valve 44 is operable ina repeatable manner.

Referring now to FIGS. 3A and 3B, bypass valve 42 is selectively movablebetween at least two distinct configurations including a restrictiveconfiguration (FIG. 3A) and bypass configuration (FIG. 3B). In therestrictive configuration, bypass valve 42 is closed and completelyprohibits pipeline fluid “F” from flowing through bypass channel 32 insome embodiments. In the bypass configuration, bypass valve 42 is atleast partially open and permits pipeline fluid “F” to flow throughbypass channel 32. Bypass valve 42 includes bypass closure member 68that is respectively movable into and out of contact with bypass seat 70to move bypass valve 42 between the restrictive and bypassconfigurations. Bypass closure member 68 is biased in an upstreamdirection toward bypass seat 70 by biasing member 72. In the illustratedembodiment, biasing member 72 is a compression spring disposed centrallywithin bypass channel 32 along longitudinal axis “A” to maintain bypassvalve 42 in the restrictive configuration until the differentialpressure reaches a pre-selected minimum bypass pressure. Thepre-selected minimum bypass pressure is defined by attributes of biasingmember 72 such as a spring constant, length and pre-load incorporatedinto the design of bypass valve 42.

Biasing member 72 is configured such that bypass valve 42 is operable tomaintain the restrictive configuration when the differential pressure inpipeline fluid “F is below the pre-selected minimum bypass pressure,operable to maintain the bypass configuration the differential pressureis above the pre-selected minimum bypass pressure, and operable to movebetween the restrictive configuration and the bypass configuration inresponse to the differential pressure reaching the pre-selected minimumbypass pressure.

When the differential pressure between upstream and downstream sides ofbypass closure member 68 reaches a pre-selected minimum bypass pressure,a force applied by biasing member 72 to maintain bypass closure member68 in contact with bypass seat 70 is overcome and bypass valve 42 opens.As the differential pressure increases beyond the pre-selected minimumbypass pressure, biasing member 72 is compressed in a proportionalmanner, thereby allowing bypass closure member 68 to move away frombypass seat 70 in a proportional manner. Thus, biasing member 72 isresponsive to the differential pressure to adjust a size of taperingconstriction 76 through which pipeline fluid “F” flows. In this manner,bypass valve 42 passively moves from the restrictive configuration ofFIG. 3A, wherein flow of pipeline fluid “F” through bypass channel 32 isrestricted, to the bypass configuration of FIG. 3B wherein the flow ofpipeline fluid “F” through bypass channel 32 is permitted. In someembodiments, the pre-selected minimum bypass pressure associated withbypass valve 42 is greater than 90 psi, and in some embodiments thepre-selected minimum bypass pressure is 100 psi. The pre-selectedminimum bypass pressure is significantly greater than the pre-selectedmaximum relief pressure described above such that bypass valve 42 movesto the bypass configuration of FIG. 3B when each relief valve 44 is inthe second closed configuration of FIG. 2C.

In the bypass configuration of FIG. 2C, bypass channel 32 and bypassvalve 42 are arranged to promote flow of pipeline fluid “F” throughbypass channel 32. Bypass channel 32 includes outer wall 74, whichdefines tapering constriction 76 with bypass closure member 68. Taperingconstriction 76 exhibits a smaller cross-sectional area than regions ofbypass channel 32 upstream and downstream of bypass closure member 68,and thus, bypass channel 32 defines a venturi to promote fluid flowtherethrough. Bypass valve 42 includes valve housing 78 defining innerwall 80 of bypass channel 32. Inner wall 80 extends in a downstreamdirection from tapering constriction 76. Bypass closure member 68 isarranged to contact inner wall 80 to form a radially decreasing profiletherewith when bypass valve 42 is in the bypass configuration. The shapeof the bypass closure member 68 and inner wall 80 compliments the shapeof outer wall 74 to guide pipeline fluid “F” into annular cavity 82,thereby discouraging turbulence and erosion of bypass channel 32. Radialfins 84 extend between outer wall 74 and housing 78 of bypass valve 42to support bypass valve 42 within bypass channel 32 and permit flow ofpipeline fluid “F” around radial fins 84.

Referring now to FIG. 4, an embodiment of a method 100 is described foruse of pipeline pig 10 (FIG. 1A). Initially, pipeline pig 10 is insertedinto pipeline “P” (step 102) through which pipeline fluid “F” isflowing. Initially, a differential pressure established in pipelinefluid “F” between trailing end 16 and a leading end 14 is below thepre-selected minimum relief pressure. Thus, relief valves 44 are in thefirst closed configuration and bypass valve 42 is in the restrictiveconfiguration. Pipeline pig 10 is propelled in a downstream direction bythe force of pipeline fluid “F” pressing on rear guide disks 20, closuremembers 50 of relief valves 44, and bypass closure member 68 of bypassvalve 42.

Next, the differential pressure is increased to the pre-selected minimumrelief pressure (step 104) thereby passively opening relief valves 44.The differential pressure is increased by various mechanisms includingincreasing a flow velocity of pipeline fluid “F” behind pipeline pig 10.In some embodiments, the differential pressure is increased by at leastpartially obstructing the pipeline pig and allowing pressure to build upbehind the pipeline pig as will be appreciated by those skilled in theart. A portion of pipeline fluid “F” is permitted to flow through reliefchannel 34 (step 106) to slow or regulate a speed of pipeline pig 10.Relief valves 44 are operable to passively move between the first closedconfiguration and the open configuration to selectively allow pipelinefluid “F” to flow through relief channels 34 to regulate the speed ofpipeline pig 10 in normal operation.

When pipeline pig 10 encounters an obstruction (step 108) however, thedifferential pressure builds up as the capacity of relief channels 34 isoverwhelmed and pipeline fluid “F” accumulates behind pipeline pig 10.The differential pressure increases to above the pre-selected maximumrelief pressure, and relief valves 44 are thereby moved to the secondclosed configuration (step 110). With the relief valves 44 in the secondclosed configuration, the full force of the buildup of pipeline fluid“F” behind pipeline pig 10 is available to push pipeline pig 10 againstthe obstruction until the obstruction is dislodged or cleared bypipeline pig 10 (step 112). Once the obstruction is cleared, reliefvalve 44 returns to the open configuration (step 114), and normaloperation resumes.

When pipeline pig 10 encounters an obstruction that cannot be cleared bya force that is safe for pipeline pig 10 or pipeline “P” (step 116) theaccumulation of pipeline fluid “F” behind pipeline pig 10 moves reliefvalves 44 to the second closed configuration and the differentialpressure increases to above the pre-selected minimum bypass pressureincreases to move bypass valve 42 to the bypass configuration (step118). Pipeline fluid “F” is permitted to flow through the single bypasschannel 32 (step 120) since flow through relief channels 34 areinterrupted by relief valves 44. Turbulence and erosion are limitedsince bypass channel 32 is larger and centrally oriented than reliefchannels 34. Pinger 24 is employable to locate pipeline pig 10, andpipeline pig 10 is retrieved from pipeline “P.”

Referring now to FIG. 5, pipeline pig 200 is constructed in accordancewith an alternate example embodiment of the invention. Pipeline pig 200is configured for active control over bypass valve 202 disposed withinbypass channel 204 and over relief valves 206 disposed within reliefchannels 208. Bypass valve 202 includes actuator 212 operable to moveclosure member 214 into and out of engagement with bypass seat 216 tomove bypass valve 202 between restrictive and bypass configurations asdescribed above. Similarly, relief valve 206 includes actuator 218operable to move closure member 220 into and out of engagement withfirst seat 222 and second seat 224 to move relief valve 206 between afirst closed configuration, an open configuration and a second closedconfiguration as described above. In the illustrated embodiment,actuators 212, 218 are hydraulic cylinders, although in otherembodiments, pneumatic or electric actuators are contemplated.

Actuators 212, 218 are in communication with controller 230, which isoperable to induce movement of actuators 212, 218 and to maintainpositions of actuators 212, 218. Controller 230 is in communication withpressure sensors 232 and 234, which are respectively disposed onupstream “U” and downstream “D” sides of bypass valve 202 and reliefvalve 206. Thus, controller 230 is operable to instruct actuator 218 tomove closure member 220 into engagement with first seat 222 if adifferential pressure detected by pressure sensors 232, 234 is less thanthe pre-selected minimum relief pressure. Also, controller 230 isoperable instruct actuator 218 to move closure member 220 intoengagement with second seat 224 if the differential pressure detected isgreater than the pre-selected maximum relief pressure, and operable toinstruct actuator 218 to move closure member 220 to an intermediateposition between first seat 222 and second seat 224 if the differentialpressure is between the minimum and pre-selected maximum reliefpressures. Similarly, controller 230 is operable to instruct actuator212 to move closure member 214 into engagement with bypass seat 216 ifthe differential pressure detected is less than the pre-selected minimumbypass pressure and operable to instruct actuator 218 to move closuremember 214 out of engagement with bypass seat 216 if the differentialpressure is greater than the pre-selected minimum bypass pressure.

In some embodiments, controller 230 is in wired or wirelesscommunication with an operator terminal (not shown) to permit anoperator to provide instructions to actuators 212, 218 independently ofpressure sensors 232, 234.

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the spirit of the present invention disclosed hereinand the scope of the appended claims.

What is claimed is:
 1. A pipeline pig, comprising: a housing defining atrailing end, a leading end and longitudinal axis extendingtherebetween; a bypass channel extending longitudinally through thehousing between the trailing end and the leading end thereof; a bypassvalve disposed within the bypass channel, wherein the bypass valve isoperable to maintain a restrictive configuration in which a pipelinefluid is prohibited from flowing through the bypass channel when adifferential pressure established in the pipeline fluid between thetrailing end and the leading end of the housing is below a pre-selectedminimum bypass pressure, and wherein the bypass valve is operable tomove to a bypass configuration in which the pipeline fluid is permittedto flow through the bypass channel in response to the differentialpressure reaching the pre-selected minimum bypass pressure; at least onerelief channel extending longitudinally through the housing between thetrailing end and the leading end thereof; and at least one relief valvedisposed within the at least one relief channel, the at least one reliefvalve operable to move from a first closed configuration to an openconfiguration in response to the differential pressure reaching apre-selected minimum relief pressure and operable to move from the openconfiguration to a second closed configuration in response to thedifferential pressure reaching a pre-selected maximum relief pressure,wherein the at least one relief valve prohibits flow of the pipelinefluid through the at least one relief channel when in the first andsecond closed configurations and permits flow of the pipeline fluidthrough the at least one relief channel when in the open configuration,and wherein the pre-selected minimum bypass pressure is greater than thepre-selected maximum relief pressure, and the pre-selected maximumrelief pressure is greater than the pre-selected minimum reliefpressure.
 2. The pipeline pig according to claim 1, wherein the at leastone relief valve includes a closure member that is respectively movablebetween first and second seats to move the at least one relief valvebetween the first and second closed configurations.
 3. The pipeline pigaccording to claim 2, wherein the closure member is biased toward thefirst seat and away from the second seat by a biasing member, such thatthe biasing member defines the pre-selected minimum relief pressure andthe pre-selected maximum relief pressure.
 4. The pipeline pig accordingto claim 3, wherein the pre-selected minimum relief pressure is in therange of 1 psi to 3 psi and the pre-selected maximum relief pressure isin the range of 4 psi to 6 psi.
 5. The pipeline pig according to claim1, wherein the pre-selected minimum bypass pressure is greater than 90psi.
 6. The pipeline pig according to claim 1, wherein the bypasschannel is centrally disposed within the housing, and wherein the atleast one relief channel includes a plurality of relief channelsradially disposed about the bypass channel.
 7. The pipeline pigaccording to claim 1, wherein the bypass channel includes a taperingconstriction therein such that the bypass channel defines a venturi. 8.The pipeline pig according to claim 7, wherein the tapering constrictionis defined between an outer wall of the bypass channel and a closuremember of the bypass valve disposed within the bypass channel, whereinthe closure member is operable to move the bypass valve between therestrictive configuration and the bypass configuration.
 9. The pipelinepig according to claim 8, wherein the bypass valve further includes abiasing member operable to maintain the closure member in contact with abypass seat to maintain the bypass valve in the restrictiveconfiguration.
 10. The pipeline pig according to claim 9, whereinbiasing member is responsive to the differential pressure to adjust thesize of the tapering constriction.
 11. The pipeline pig according toclaim 7, wherein the bypass valve includes an inner wall extendingthrough at least a portion of the bypass channel, and wherein theclosure member is arranged to form a tapered profile with the inner wallwhen the bypass valve is in the bypass configuration.
 12. A pipelinepig, comprising: a housing defining a trailing end, a leading end andlongitudinal axis extending therebetween; at least one relief channelextending longitudinally through the housing between the trailing endand the leading end thereof, the at least one relief channel defining anannular wall; a closure member disposed within the annular wall, theclosure member operable to engage a first seat to prohibit fluid flowthrough the relief channel and operable to disengage the first seat topermit fluid flow through the relief channel; and an annular spacedefined between the closure member and the annular wall, the annularspace exhibiting a smaller cross-section than regions of relief channelupstream and downstream of the closure member such that the annularspace represents a constriction for fluid flow and the relief channeldefines a venture, wherein the closure member is further operable toengage a second seat to prohibit fluid flow through the relief channelwhile the closure member is disengaged from the first seat, and whereinthe closure member is biased toward the first seat and away from thesecond seat by a biasing member, such that the biasing member isoperable to passively maintain the closure member in engagement with thefirst seat if a differential pressure established between a trailing endand a leading end of the housing is less than a pre-selected minimumrelief pressure, and operable to permit the closure member to engage thesecond seat if the differential pressure is greater than a pre-selectedmaximum relief pressure.
 13. The pipeline pig according to claim 12,further comprising a bypass channel and a bypass valve, wherein thebypass channel extends longitudinally through the housing between thetrailing end and the leading end thereof, and wherein the bypass valveis operable to selectively move between restrictive and bypassconfigurations to respectively prohibit and permit fluid flow throughthe bypass channel.
 14. The pipeline pig according to claim 13, whereinthe bypass valve is operable to move from the restrictive configurationto the bypass configuration in response to the differential pressurereaching a pre-selected minimum bypass pressure, and wherein thepre-selected minimum bypass pressure is greater than the pre-selectedmaximum relief pressure such that the bypass valve moves to the bypassconfiguration while the closure member is engaged with the second seatand fluid flow through the at least one relief channel is restricted.15. The pipeline pig according to claim 12, wherein the closure memberis operably coupled to an actuator, and wherein the actuator is operableto move the closure member into engagement with the first seat when adifferential pressure established between a trailing end and a leadingend of the housing is less than a pre-selected minimum relief pressure,and operable to move the closure member into engagement with the secondseat when the differential pressure is greater than a pre-selectedmaximum relief pressure.